1. Field of the Invention
The present invention relates to an authenticity indicator for indicating the authenticity of an article or the like.
2. Background Art
Authenticity indicators (identification media) for indicating the authenticity of articles or the like have been attached to objects as a means of preventing forgery of cards, passports, identification cards, gift certificates, etc. or of detecting forgeries, fakes, etc. Namely, the authenticity of objects to which authenticity indicators are attached is confirmed by checking the authenticity of the authenticity indicators themselves. It is therefore necessary that the authenticity indicators cannot be easily forged and that the authenticity of the authenticity indicators themselves can be checked accurately.
Hologram labels using relief holograms have been known as the above-described authenticity indicators. In recent years, however, techniques for forgery of holograms of this type have advanced, and holographic materials have become easily available, so that there are possibilities that the hologram labels might be skillfully forged and that the forged hologram labels might be overlooked while they are practically used.
Cholesteric liquid crystals, which have both polarized-light selectivity and wavelength selectivity and which reflect light so that the reflected light changes in color when an observer changes his viewing angle, have also been used for authenticity indicators. However, forgery techniques have advanced in recent years, and even authenticity indicators using cholesteric liquid crystals are in danger of forgery.
The Japanese Patent Publication No. 3652487 (the entire contents of this patent publication are incorporated herein by reference) discloses identification media (authenticity indicators) comprising a relief hologram layer and a cholesteric liquid crystal layer.
In the identification media disclosed in the above patent publication, however, the cholesteric liquid crystal layer acts merely as reflective layer for reflecting incident light to the relief hologram layer. Further, the authenticity of the identification media can be confirmed only on the basis of the images reconstructed from the relief holograms. Moreover, relief holograms have come to be forged as described above. Thus, although the production of these identification media costs much labor, their distinguishability and forgery prevention effect are comparable only to those of the above-described authenticity indicators using either relief holograms or cholesteric liquid crystals alone.